The present invention relates to an optical head for use in optical recording/reproducing apparatus such as optical disk equipment and, more particularly, to a separation type optical head having a stationary section such as a light source unit and a movable section such as a lens system, which sections are constructed separately.
A separation type optical head has been known which has a stationary section and a movable section separated from each other, wherein only the movable section moves in the radial direction of a disk across tracks formed on the disk. This type of optical head is disclosed, for example, in Japanese Patent Unexamined Publication No. 62-267936 and also in "Comprehensible Optical Disk" (page 159) published by Opto-Electronics Co., Ltd.
In the known separation type optical head, the stationary section includes components such as a laser diode, a beam splitter and a photo-detector, while the movable section includes components such as a mirror, objective lens and a mechanism for driving such components. Thus, the movable section of the separation type optical disk has a smaller size and weight than the optical head of non-separation type. Therefore, the separation type optical disk offers a reduction in the size of the access mechanism, as well as increased access speed.
On the other hand, the separation type optical head suffers from a problem in that the movable section tends to be tilted in the direction of movement and in the directions transverse to the direction of movement, during the radial movement of the movable section across tracks. Tilting of the movable section, in particular tilting in the direction of movement, causes a relative positional offset of the optical components with the result that the light ray impinging upon the optical disk and the light ray reflected from the optical disk diverge from each other, resulting in an offset of a tracking servo signal. This phenomenon will be referred to as "divergence of light".
More specifically, when there is no tilting of the movable section, the light ray which passes through the optical axis perpendicularly impinges upon the recording surface of a disk and is reflected back along the same path as the incident ray. However, if the movable section is tilted, the light ray impinges upon the disk at an inclination, so that the divergence of light is produced to cause the reflected ray to fail to impinge upon the correct or predetermined portion of the photodetector, thus causing an offset of the tracking servo signal. Such an offset of the tracking servo signal makes it impossible to detect any tracking offset, i.e., any offset of the incident ray from the center of the aimed track. Alternatively, a track error signal is generated even though there is no tracking offset.